How does one correct the keyword -asdf -asdf issue

Site ranks well with the negative nonsense words

[sahuman]

My sites went down to the #14 page from the #1 page since December. However, I still find these sites on Page 1 of SERPS when searched with the old trick of inserting negative keywords.

keyword -asdf -asdf -asdf -asdf -asdf -asdf -asdf -asdf -asdf -asdf -asdf -asdf -asdf

All my 5 sites are cross-linked, have backlinks (from sites that do not belong to me) but have no spammy SEO techniques.

Is there anything I can do to correct things with Google?

However, my sites are doing very well with yahoo and MSN Beta.